A typical Tomcat installation includes a "class-loader-howto.html" file which explains in detail how Tomcat finds and loads classes. Study it.

IF your class name is registration (small initial character - bad practice, use initial Cap to keep classes clearly differentiated from packages)
THEN under WEB-INF/classes, tomcat expects a com subdirectory having a servlet subdirectory having a registration.class file.

Furthermore, under WEB-INF there must be the valid web.xml file.

Why did you try such odd-ball things as a com/classes directory or classes/servlet1 when the package appears to be "com.servlet"